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39 lines
721 B
C
39 lines
721 B
C
#include <math.h>
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#include <stdio.h>
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#define NRANSI
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#include "nrutil.h"
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void polint(double xa[], double ya[], int n, double x, double *y, double *dy)
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{
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int i,m,ns=1;
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double den,dif,dift,ho,hp,w;
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double *c,*d;
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dif=fabs(x-xa[1]);
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c=dvector(1,n);
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d=dvector(1,n);
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for (i=1;i<=n;i++) {
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if ( (dift=fabs(x-xa[i])) < dif) {
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ns=i;
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dif=dift;
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}
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c[i]=ya[i];
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d[i]=ya[i];
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}
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*y=ya[ns--];
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for (m=1;m<n;m++) {
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for (i=1;i<=n-m;i++) {
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ho=xa[i]-x;
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hp=xa[i+m]-x;
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w=c[i+1]-d[i];
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if ( (den=ho-hp) == 0.0) nrerror("Error in routine polint");
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den=w/den;
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d[i]=hp*den;
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c[i]=ho*den;
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}
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*y += (*dy=(2*ns < (n-m) ? c[ns+1] : d[ns--]));
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}
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free_dvector(d,1,n);
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free_dvector(c,1,n);
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}
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#undef NRANSI
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